Steel cable barriers in highway medians are a low cost way to improve traffic safety without busting state department of transportation budgets. Cable barriers cost $44,000 per mile, compared with $72,000 per mile for guardrail and $419,000 per mile for concrete barriers. Furthermore, cable barriers tend to snag tractor-trailer rigs, keeping them from ricocheting back into same-direction traffic.
The state of Ohio spent $4.97 million installing 113 miles of cable barriers.

(a) If the cables prevent accidents totaling $1.3 million per year, determine the rate of return that this represents over a 10-year study period. Use all three methods—
tabulated factors, a calculator, and a spreadsheet.

(b) Now, determine the rate of return for 113 miles of guardrail if accident prevention is $1.1 million per year over a 10-year study period. To do so, first write the ROR relation and then find i* using a single-cell spreadsheet function.